Semiconductor package having light sensitive chips

ABSTRACT

A microelectronic package includes a light sensitive microelectronic element having a front face including one or more contacts and a rear surface, and conductive leads having first ends connected to the one or more contacts and second ends connected to one or more conductive pads adjacent the light sensitive microelectronic element. The package also includes an at least partially transparent encapsulant covering the light sensitive microelectronic element, the conductive leads and the one or more conductive pads, whereby the one or more conductive pads are exposed on a surface of the encapsulant.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/342,973, which is a continuation of U.S. patent applicationSer. No. 09/025,558, which claims benefit of U.S. ProvisionalApplication 60/038,214, filed Feb. 18, 1997, and is related to U.S.patent application Ser. No. 08/634,464 filed Apr. 18, 1996, thedisclosures of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention generally relates to microelectronic assemblies,and more specifically it relates to semiconductor chip packages havinglight sensitive or light emitting chips.

The semiconductor chip packaging industry is a highly competitivebusiness in which the packaging companies are waging an on-going battleto improve the reliability and cost of packaged chips. Moreover, theelectronics industry continues to demand that chip packages take up lessspace within electronic components. As such, it is desirable that theoverall size of the packaged chips be reduced so that the same circuitryfits into smaller areas thereby allowing for more portability (size,weight, etc.) for the resulting finished electronic product and/orallowing for an increase in a product's processing power without alsoincreasing its size.

One type of semiconductor chip package includes packages whichincorporate light sensitive semiconductor devices such as integratedcircuits. When packaging such light sensitive devices (referred toherein as “IC's” or “chips”), it is necessary to allow for the passageof visible or near visible light, i.e. ultraviolet (“UV”) or infrared(“IR”) light, to the surface of the packaged chip. For example,ultraviolet-erasable programmable read-only memories (“UV EPROMS”) havetraditionally been manufactured using a standard lead frame typepackage, as shown in FIG. 1. Typically in this type of package, a cavityis molded (as by an injection molding operation) around a lead frame andthe back surface of the chip is attached to a paddle on the lead frame.The chip contacts on the face surface of the chip are then wire bondedto respective leads on the lead frame. This allows the chip assembly tobe enclosed on three sides. The fourth side of the assembly is thenfitted with a transparent lid made of glass or quartz so that the chipis physically protected but still capable of receiving light through thelid.

In a similar fashion, when packaging certain light emitting chips suchas light emitting diodes (LED's), it is desirable to allow for thepassage of visible or near visible light from a surface of the packagedchip. When manufacturing light emitting diodes, the LED's are commonlycreated on leadframe like structures. As shown in FIG. 2, anelectrically conductive back surface of the chip is typically attachedto an electrically conductive base on a first lead and chip contacts ona face surface of the chip are wire bonded to corresponding secondleads. The base of the first lead typically has a notch within which thechip sits. The assembly is then encapsulated by using an injectionmolding technique. The encapsulant may form a lens on the top of the LEDpackage to aid in the focusing of the light being emitted from the chip.

U.S. Pat. No. 4,890,383 to Lumbard et al. discloses another techniquefor packaging LED's which use a supporting frame or substrate as part ofthe package structure. As set forth in the '383 patent, the substratecomprises an electrically insulating material such as synthetic plastic.The top surface of the substrate includes a conductive pattern whichdefines a land area and a connection pad. A light emitting diode ismounted on the land area so that its terminal underneath is electricallyand mechanically connected to the land area. The upper side of the lightemitting diode is provided with a terminal which is electricallyconductive and connected with the connection pad via a bonding wire.

A second conductive pattern of highly conductive material such as copperis deposited onto the rear surface of the substrate. This secondconductive pattern defines a first terminal pad and a second terminalpad. The land area on the top side of the substrate is provided with anextension which is electrically connected to the terminal pad on theunder side via a plated through groove having a semicircularcross-section. Similarly, the connection pad on the upper side of thesubstrate is provided with an extension which is electrically connectedto the terminal pad on the under side via a plated through groove, whichis preferably identical to the plated through groove. In this manner thetwo terminal pads serve as external terminals for the light emittingdiode which mechanically secures modular component during surfacemounting of the component. The assembly is provided with a transparentcovering for protective purposes. Thus the light emitting diode and itselectrical contacts including the bonding wire are sealed andencapsulated in the covering. The covering is made from clear ordiffused epoxy, which provides optical characteristics.

Despite these and other efforts in the art, still further improvementsin interconnection technology would be desirable. The chip packagesmanufactured in accordance with the prior art methods described abovetypically consume greater areas on a printed circuit board or within anelectronic component than might otherwise be required. In addition,these particular prior art embodiments are also relatively complex andexpensive.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method of making amicroelectronic package having an optoelectronic element, such as alight sensitive or light emitting semiconductor chip, includes providinga sacrificial layer having a first surface and one or more conductivepad areas. One or more conductive pads and a base may be selectivelyformed on the first surface of the sacrificial layer, preferably byusing photolithographic techniques. In certain embodiments, the base mayinclude a conductive material, such as an electrically conductivematerial. The base and pads are preferably formed using electroplatingtechniques, whereby the base is located within a central region definedby the conductive pads. After the base and the one or more conductivepads have been formed, the optoelectronic element is provided. Theoptoelectronic element may have a front face including a plurality ofcontacts and an optical area for receiving incoming light and a rearsurface. The rear surface of the optoelectronic element may then bejuxtaposed and attached to the top surface of the base by preferablyusing an adhesive such as a thermally conductive adhesive. Next, thecontacts may be electrically interconnected with the one or moreconductive pads on the sacrificial layer using wire bonding techniques.In one preferred embodiment, the wire bonding step includes providingconductive wires having first and second ends, bonding the first ends ofthe wires to the contacts and bonding the second ends of the wires tothe conductive pads. Other elements which may be used to interconnectthe contacts and the conductive pads include electroformed beam leadsand tape-automated bonding leads (TAB leads). Next, a curable and atleast partially transparent encapsulant is provided over the firstsurface of the sacrificial layer so as to encapsulate the base, theoptoelectronic element and the one or more conductive pads and theencapsulant is cured. As used herein, the term “at least partiallytransparent” means a material that allows any amount of light to passtherethrough and includes the terms light transmissive, transparentand/or translucent. In certain preferred embodiments this term means amaterial transparent to one or more desired wavelengths of light. Forexample, the material may be transparent to certain wavelengths of lightand opaque to other wavelengths of light. After the curing step thesacrificial layer is at least partially removed so as to leave the baseand the one or more conductive pads exposed and/or accessible at abottom surface of the encapsulant. The bottom surface of the encapsulantpreferably defines the bottom of the package. In certain preferredembodiments the base and the one or more conductive pads protrudeslightly beyond the bottom surface of the encapsulant so that thepackage may be readily interconnected with an external circuit elementsuch as a PCB. In other preferred embodiments, a base is not used tomake the package and the rear surface of the optoelectronic element isattached directly to the first surface of the sacrificial layer duringfabrication of the package so that after the sacrificial layer isremoved the rear surface of the optoelectronic element is exposed and/oraccessible at the bottom of the package. As such, the rear surface ofthe chip may be directly connected to an external element, such as aheat sink or a PCB. In still other embodiments, the base and/or the oneor more conductive pads may be formed from the sacrificial layer.

The method described above may also include the step of placing a lid ata top surface of the encapsulant so that the lid overlies the front faceof the optoelectronic element. The lid is preferably transparent or atleast partially transparent and is preferably selected from the groupconsisting of glass, quartz and rigid polymeric materials. In certainpreferred embodiments, the lid is formed separately from the package andis attached to the top surface of the encapsulant. In other embodimentsthe lid may be integrally formed with the top surface of theencapsulant. The lid may include a coating for filtering out certainfrequencies of light. The lid may also include a lens for focusingincoming light onto the optical area on the front face of theoptoelectronic element. The lens may be of any type, such as aFresnel-type lens or a telescopic-type lens. In certain preferredembodiments, the top surface of the lid, which is remote from the frontface of the optoelectronic element, is provided with a connector. Theconnector preferably secures an end of a light transmitting cable on thetop surface of the lid so as to focus light from the light transmittingcable through the transparent lid and onto the optical area on the frontface of the optoelectronic element. The connector may be integrallyformed with the lid and may include a cavity for receiving and securingthe end of the light transmitting cable.

In other preferred embodiments, a plurality of microelectronic packagesmay be manufactured simultaneously on the same sacrificial layer usingthe techniques described above. In these embodiments after the packageshave been formed, individual packages are provided by severing thesacrificial layer to provide individual microelectronic packages. Inother embodiments, the separating step provides a plurality of multichipmodules whereby each module includes two or more of the optoelectronicelements.

In a further embodiment of the present invention, a method of making amicroelectronic package includes the steps of providing an electricallyconductive sheet and forming a conductive base having a cavity formedtherein and at least one conductive pad adjacent the conductive base,the cavity having a light reflective surface. Portions of the conductivesheet may be removed using photolithographic and etching techniques. Inother embodiments the conductive pads and conductive base may be formedusing a die or stamping machine. The cavity is preferably a depressionformed into the first surface of the electrically conductive sheet andmay include a bottom portion and side walls extending therefrom. Thebottom portion and the side walls of the cavity and the at least oneconductive pad may be covered with a layer of a non-oxidizingelectrically conductive material, such as silver or gold. Although bothsilver and gold may be used as effective electrically conductive layers,silver is more preferred because it is relatively more reflective thangold. In other embodiments, the electrically conductive material mayalso be provided over the second surface of the conductive sheet atlocations in alignment with the conductive pad and the cavity. Anoptoelectronic element, such as a light emitting chip or light emittingdiode (LED), having a front face including at least one contact and arear surface having at least one contact is provided and the rearsurface of the optoelectronic element is attached to the base so as toposition the optoelectronic element in the cavity and electricallyinterconnect the optoelectronic element and the conductive base. Next,the at least one contact on the front face of the optoelectronic elementmay be electrically interconnected with the at least one conductive padsuch as by using the wire bonding techniques described above. A curableand at least partially transparent or translucent encapsulant may thenbe provided over the first surface of the conductive sheet so as toencapsulate the at least one conductive pad, the conductive base and theoptoelectronic element. The encapsulant is then cured. In preferredembodiments the encapsulant can be cured by using heat, UV light, atwo-part reacting mixture or curing at room temperature. After thecuring step, additional portions of the conductive sheet may beselectively removed so as to electrically isolate the conductive basefrom the at least one conductive pad. The assembly may then beelectrically interconnected with an external circuit element byconnecting the conductive base and the at least one conductive pad tocontacts on the external circuit element.

In certain preferred embodiments of the present invention theencapsulant has different levels of transparency or translucency. Forexample, in one particular preferred embodiment the encapsulantoverlying the optical area of the optoelectronic element is moretransparent than the encapsulant overlying the periphery thereof. Theencapsulant may also include a compliant material whereby the gradientof compliancy varies throughout the package. In one particularembodiment the encapsulant adjacent the chip contacts is more compliantthan the encapsulant adjacent the at least one conductive pads. Thisparticular feature enables the conductive wires or leads adjacent thecontacts to readily flex and move as the light sensitive chip or lightemitting chip expands and contracts during operation. In still otherpreferred embodiments the encapsulant includes a color tinted portionfor changing the color of the emitted light as perceived by an observer.For example, the light emitted from the optoelectronic element may bered and the encapsulant may have a blue tint so that the emitted lightas perceived by an observer is purple.

Certain preferred embodiments of the present invention provide near“chip size” microelectronic packages having light sensitive or lightemitting chips whereby the overall size of the package is not muchlarger than the size of the chip itself. Thus, the final packages have asmaller footprint and will take up less space on a circuit board orwithin an electronic component which enables the overall size of thefinal electronic product to be reduced. This is a dramatic advance overprior art packages which teach using bulky substrates which generallydwarf the size of the chip so as to create packages which are muchlarger than the chip being packaged, thereby wasting a significantamount of space within an electronic device. The present invention alsoprovides methods for mass producing reliable and economical chippackages.

In yet another embodiment of the present invention, a method of making amultichip module having a plurality of optoelectronic elements includesthe steps of providing a substrate having a dielectric layer disposedbetween a top conductive layer and a bottom conductive layer andselectively removing portions of the bottom conductive layer to form anarray of conductive pads. Portions of the top conductive layer and thedielectric layer are then selectively removed to form an array ofopenings extending through the top conductive layer and the dielectriclayer, whereby the array of openings are in alignment with theconductive pads. A plurality of optoelectronic elements, such as lightemitting semiconductor chips, are then provided over the top conductivelayer and electrically interconnected with the top conductive layer.Each optoelectronic element preferably includes a front face having acontact and a rear surface having a contact, whereby the rear surface ofeach optoelectronic element is preferably attached to the top conductivelayer. The rear surfaces may be attached by applying an electricallyconductive adhesive over the top conductive layer and abutting the rearsurfaces of the optoelectronic elements against the electricallyconductive adhesive. Each optoelectronic element may also beelectrically interconnected with one of the conductive pads such as byusing flexible conductive leads or wires to interconnect the contacts onthe front face of the optoelectronic elements and the conductive pads. Acurable and at least partially transparent encapsulant is then providedover the top conductive layer and the plurality of optoelectronicelements and the encapsulant is cured. A transparent lid which overliesthe optoelectronic elements may be attached over a top surface of theencapsulant layer.

The foregoing and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe preferred embodiments set forth below, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a prior art chip package including a lightsensitive chip.

FIG. 2 shows a side view of a prior art chip package including a lightemitting chip.

FIGS. 3A-3I show a side view of a method of making a microelectronicpackage including one or more optoelectronic elements according to oneembodiment of the present invention.

FIG. 4A shows a perspective side view of a microelectronic packageincluding an optoelectronic element made in accordance with the methodshown in FIGS. 3A-3I.

FIG. 4B shows a side view of another embodiment of a microelectronicpackage including an optoelectronic element made in accordance with themethod shown in FIGS. 3A-3I.

FIG. 5 shows a perspective side view of a microelectronic packageincluding an optoelectronic element made using the method shown in FIGS.3A-3I according to another embodiment of the present invention.

FIGS. 6A-6G show a side view of various lids including lenses which maybe used with the microelectronic packages shown in FIGS. 3-5 accordingto various embodiments of the present invention.

FIGS. 7A-7K show a side view of another method of manufacturing amicroelectronic package including an optoelectronic element according toyet another embodiment of the present invention.

FIG. 7H′ shows a microelectronic package including an optoelectronicelement according to another preferred embodiment of the presentinvention.

FIGS. 8A and 8B show respective perspective and cross-sectional sideviews of a microelectronic package including an optoelectronic elementmade in accordance with the method shown in FIGS. 7A-7K.

FIGS. 9A-9E show a side view of a method of making a microelectronicpackage including an optoelectronic element according to still furtherembodiments of the present invention.

FIG. 10 shows a side view of another embodiment of a conductive padstructure shown in FIGS. 9A-9H according to another embodiment of thepresent invention.

FIG. 11 shows a side view of still another embodiment of the conductivepost structure shown in FIGS. 9A-9H according to another embodiment ofthe present invention.

FIGS. 12A-12F show a side view of a method of making a multichip moduleincluding a plurality of optoelectronic elements according to stillanother embodiment of the present invention.

DETAILED DESCRIPTION

FIGS. 3A through 3I show a method for making a package having asemiconductor chip such as a light sensitive chip, according to onepreferred embodiment of the present invention. The method described issomewhat similar to the process disclosed in U.S. patent applicationSer. No. 08/634,464, filed on Apr. 18, 1996, the disclosure of which ishereby incorporated by reference herein. As shown in FIG. 3A, asacrificial layer 20 is provided having a first surface 22 and a secondsurface 24. The sacrificial layer 20 may include a conductive metallicmaterial, a polymer material or a combination of both. Specific examplesof preferred sacrificial layer materials include aluminum, copper,steel, iron, bronze, brass, polyimide, polyetherimide, flouropolymer andalloys and combinations thereof. In the particular embodiment shown inFIG. 3A, the sacrificial layer 20 includes a sheet of aluminum having anapproximate substantially uniform thickness of about 100-200 microns;although, the sacrificial sheet could be thicker or thinner in someembodiments. Referring to FIG. 3B, photolithographic techniques are usedto define a pattern over the first surface 22 of the sacrificial layer20. Preferably a photo-resist layer 25 is formed over the first surface22 of the sacrificial layer 20 and apertures are developed and removedusing photolithographic techniques. Referring to FIG. 3C, next a base 26and a plurality of conductive pads 28 are deposited or electroplatedwithin the apertures in the photo-resist layer 25 on the first surface22 of the sacrificial layer 20. The particular embodiment shown in FIG.3C shows two such bases 26 with each base 26 surrounded by two or moreconductive pads 28. The conductive pads 28 generally define a centralregion 30 therebetween and the base 26 is formed in the central region30. Referring to FIGS. 3C and 3D, the remainder of the photo-resistlayer 25 is removed from the first surface 22 of the sacrificial layer20 to leave behind one or more bases 26 whereby each base 26 issurrounded by conductive pads 28 associated therewith.

Referring to FIG. 3E, an optoelectronic element such as a lightsensitive integrated circuit 32 having a front face 34 including anoptical area 36 for receiving light is then juxtaposed with a topsurface 38 of the base 26. Each light sensitive chip 32 preferablyincludes a plurality of contacts 33 on the front face 34 and a rearsurface 40. The rear surface 40 of the chip 32 is preferably attached tothe top surface 38 of the base 26 using a thermally conductive adhesivematerial 41, typically comprised of metal loaded thermoset orthermoplastic materials. Referring to FIG. 3F, the contacts 33 on thefront face 34 of the chip 32 are then electrically connected to theirrespective conductive pads 28, typically using a standard wire-bondingoperation. In FIG. 3F, the electrical connections are made by using awirebonder to stitch bond first ends 42 of a flexible, conductive wire44 to the conductive pads 28 and second ends 46 of the wire 44 to thechip contacts 33. The stitch bonds create a low profile electricalconnection between the contacts 33 and the conductive pads 28 which,inter alia, results in the final package being thinner. The wirebondedconnection may take the form of a ball bond/stitch (or wedge) bondcombination, as shown in FIG. 3F. Other elements which may be used tointerconnect the chip contacts 33 and the conductive pads 28, includeTAB leads and electroformed beam leads.

Referring to FIG. 3G, the entire assembly is then encapsulated using aflowable, curable encapsulant 48, such as by using an injection moldingoperation. The encapsulant 48 preferably covers the top surface 22 ofthe sacrificial layer 20 and encapsulates the optoelectronic element 32,the base 26, the conductive pads 28 and the wires 44. The curableencapsulant 48 typically includes filled or unfilled standard thermosetor thermoplastic resins as used in industry, such as epoxy resin,silicone resin or other plastic encapsulating material. The encapsulant48 is then cured so as to provide structural integrity to the chippackage as well as providing the boundaries of the package. Theencapsulant 48 is preferably transparent or at least partiallytransparent so that light may pass through the encapsulant 48 and bereceived within the optical area 36 on the front face 34 of theoptoelectronic element 32. However, in other embodiments the encapsulant48 may be fairly opaque depending upon the amount or wavelength of lightneeded to reach the chip 32. In certain embodiments the level oftransparency of the encapsulant 48 may change throughout the package sothat the encapsulant 48 in one portion of the package is more or lesstransparent than the encapsulant 48 in another portion of the package.For example, the encapsulant 48 overlying the optical area 36 of theoptoelectronic element 32 may be more transparent than the encapsulant48 overlying peripheral portions of the chip 32. As mentioned above, theterm “at least partially transparent” means a material that allows anyamount of light to pass therethrough and includes the terms lighttransmissive, transparent and/or translucent. The terminology “at leastpartially transparent” may also be defined as a material which istransparent to one or more desired wavelengths of light (e.g. UV or IRlight). For example, the material may be transparent to certainwavelengths of light and opaque to other wavelengths of light so thatonly desired wavelengths of light may pass through the material to theoptoelectronic element.

The encapsulant 48 also preferably includes a compliant material, suchas a silicone elastomer so that the conductive wires 44 may flex andbend during operation of the package. This will enhance the ability ofthe flexible wires 44 or leads to remain electrically connected to thecontacts 33 and conductive pads 28 during expansion and contraction ofthe package elements. In some embodiments, it may be preferable to varythe level of compliancy of the encapsulant 48 throughout package so thatcertain portions of the wire 44 flex more easily than other portions ofthe wire 44. For example, referring to FIG. 3H, the encapsulant 48 maybe more rigid near the bottom 50 of the package where the first ends 42of the wires 44 are attached to the conductive pads 28 and relativelymore compliant near the top 52 of the package where the second ends 46of the wires 44 are attached to the chip contacts 33 so that the wires44 may readily flex and bend during expansion and contraction of thechip 32. In still other preferred embodiments the encapsulant 48 mayinclude a color tinted portion for changing the color of the lightgenerated by the chip as perceived by an observer.

Referring back to FIG. 3G, after the optoelectronic element 32 has beenelectrically connected to the conductive pads 26, a lid 54 may be placedat a top surface 52 of the package assembly. Preferably the lid 54 isjuxtaposed with the front face 34 of the chip 32. The lid 54 is thenattached to the top surface 52 of the encapsulant 48 which also happensto be the top of the package. The lid 54 is preferably transparent andmay be made of any suitable transparent material, such as glass, quartz,and rigid polymeric materials. The lid 54 may also be made using amolding operation as opposed to attaching a separately formed lid. Thelid 54 may be integrally molded simultaneously with the encapsulant 48so that the lid 54 has special surface features. In this latterembodiment, the lid 54 may be juxtaposed with the chip 32 and thecurable liquid encapsulant may be introduced between the lid 54 and thechip 32. In certain embodiments, the lid 54 may include a coatingapplied to the surface thereof for filtering certain frequencies oflight. In other preferred embodiments, light reflective or lightfocusing elements such as transparent beads or spheres may be used inplace of a lid. The transparent beads or spheres, which may compriseplastic or glass, are preferably provided in the encapsulant, preferablybefore the encapsulant is cured, so that one or more of the lightfocusing elements are aligned with one or more optoelectronic elements.The beads or spheres may have different light reflective properties. Asmentioned above, the beads or spheres typically replace the lidsdescribed above and their use will generally result in a significantcost savings.

Referring to FIG. 3H, the sacrificial layer 20 is next removed,preferably using an etching operation to expose the conductive pads 28and the base 26 at the bottom surface 50 of the encapsulant 48, whichalso happens to be the bottom of the package. If desired, thesacrificial layer may be selectively removed to provide added featureson the bottom of the finished package, such as taller conductive pads 28which protrude from the encapsulant 48 at the bottom of the package,and/or a heat sink (not shown) disposed beneath and protruding from thebottom 50 of the package and connected to the bottom surface 56 of thebase 26.

Referring to FIG. 3I, after the sacrificial layer 20 has been removed,the assembly may then be separated into individual packages having oneoptoelectronic element or into multichip modules having two or moreoptoelectronic elements. At this point, the exposed conductive pads 28may be attached to respective bond pads on an external circuit element(not shown), such as a printed circuit board, using conventional solderballs. The solder balls preferably comprise a combination of tin andlead and may further include a conductive or non-conductive core.Typically, the bottom surface 56 of the base 26 is connected to theprinted circuit board in such a way that heat is drawn away from thechip 32 and into the printed circuit board during operation of thepackage. The multichip package embodiment may include chips of differentsizes which perform different functions.

FIG. 4A shows a perspective side view of one preferred embodiment of apackage 10 including an optoelectronic element, such as a lightsensitive chip 32, which has been manufactured using the techniquesdescribed immediately above. The package 10 includes a base 26 having atop surface 38 whereby a rear surface 40 of the light sensitive chip 32is attached to the top surface 38 of the base 26 by a thermallyconductive adhesive 41. The chip 32 includes a front face having aplurality of contacts (not shown) which are connected to electricallyconductive pads 26 by flexible, conductive wires 44. An at leastpartially transparent or translucent encapsulant layer 48 is providedover the chip 32. The encapsulant 48 provides structural integrity tothe package 10. The conductive pads 28 and the base 26 are accessible ata bottom surface 50 of the package 10 and at the bottom of theencapsulant 48. An at least partially transparent lid 54 is juxtaposedwith the front face 34 of the chip 38 and attached to the top surface 52of the encapsulant 48. The lid 54 enables light to pass therethrough,through the at least partially transparent encapsulant 48 and onto theoptical area 36 on the front face 34 of the chip 32.

FIG. 4B shows a side view of another preferred embodiment of a package10′ which has been manufactured using most of the techniques describedabove. However, in this particular embodiment, a base (as shown in FIG.3C) is not provided over the first surface of the sacrificial layerbefore the optoelectronic element 32′ is attached. The optoelectronicelement 32′ includes a front face 34′ having contacts 33′ and opticalarea 36′. Conductive wires 44′ electrically interconnect contacts 33′and conductive pads 28′. An at least partially transparent lid 54′ isattached to top surface 52′ of encapsulant 48′. The rear surface 40′ ofthe optoelectronic element 32′ is secured directly to the first surfaceof the sacrificial layer and the remaining processing steps are followedas described above. In this particular embodiment, the one or moreconductive pads 28′ may be part of the sacrificial layer with theconductive pads being left behind when portions of the sacrificial layerare removed. After the sacrificial layer is removed, the rear surface40′ of the optoelectronic element 32′ is exposed and accessible at thebottom 50′ of the package 10′ whereby the rear surface 40′ may beattached directly to an external element such as a heat sink or aprinted circuit board.

FIG. 5 shows another embodiment of the present invention including apackage which is substantially similar to that shown in FIG. 4A. Thepackage 110 includes encapsulant 148 and a lid 154 having a focusinglens 160 used to focus incoming light onto the optical area 136 on thefront face 134 of the optoelectronic element 132. The lens 160 may beintegrally formed with the lid 154 during the molding operationdiscussed above. The lens 160 preferably focuses the light transmittedto or from the optical area 136 of the chip 132. The lid 154 may alsohave a connector 162 accessible at the top surface 164 thereof forsecuring a fiber optic cable or other suitable light transmitting cableto the top of the lid 154. The connector 162 preferably has a cavity 166formed therein so the light transmitting cable may be inserted into thecavity 162 so as to more accurately align the cable with the lens andwith the optical area 136 of the chip 132. In further embodiments, theconnector 162 may be formed using a molding operation so that theconnector 162 is an integral portion of the lid.

Referring to FIGS. 6A-6G, the lens 160 within the lid 154 may be of anystructure that is beneficial to the particular light sensitiveapplication. FIGS. 6A-6F show a variety of lenses that could be used inthis chip package. FIG. 6G shows a lid 254 having a Fresnel type lens260.

FIGS. 7A-7K show another embodiment of the present invention including aprocess for making microelectronic packages having one or moreoptoelectronic elements such as light sensitive (e.g. UV EPROM) or lightemitting chips. The particular chip shown in FIGS. 7H through 7K is alight emitting diode (LED). Referring to FIG. 7A, an electricallyconductive sheet 320 includes a conductive material such as copper.Referring to FIG. 7B, both the first and second surfaces 322 and 324 ofthe conductive sheet 320 are next coated with photoresist 325 which isexposed and developed using standard photolithographic techniques.Referring to FIG. 7B, certain portions of the photoresist 325 overlyingthe first surface 322 of the conductive sheet 320 are then removed toexpose portions of the first surface 322 of the conductive sheet 320.Referring to FIG. 7C, the exposed first surface 322 of the conductivesheet 320 is then etched in a suitable etchant so that a desired amountof the conductive sheet 320 is removed to provide one or more cavities368 surrounded by conductive pads 328. Referring to FIG. 7D, thephoto-resist 325 is then removed from the first and second surface 322,324 of the conductive sheet 320 leaving the conductive sheet 320 withthe desired surface topology on the first surface 322 thereof. Referringto FIG. 7D, each cavity 368 preferably includes a bottom 370 and sidewalls 372. Referring to FIGS. 7E-7G, a non-oxidizing electricallyconductive layer 374 may be selectively electroplated over the cavities368 and the conductive pads 328 on the first surface 322 of theconductive sheet, as well as on the second surface 324 of the conductivesheet 320 at locations which are in alignment with the cavities 368 andthe conductive pads 328. Typically, the non-oxidizing layers includeconductive metal materials such as silver or gold. The electricallyconductive layer 374 preferably enhances the reflection of light fromthe cavity 368.

As shown in FIG. 7H, one or more LED's 332 are then juxtaposed with theconductive layer 374 overlying each cavity 368. As shown in FIG. 7H′each LED chip 332 preferably has a front face 334 including a firstcontact 376 and a rear face 340 including a second contact 378. The rearsurfaces of the LED chips 332 are then attached to the bottom 370 oftheir respective cavities 368 so as to position the optoelectronicelements in the cavity and so that the second contact 378 iselectrically connected to the conductive layer 374. As shown in FIG.7H′, the cavity 368 is preferably deeper than the chip 332 is thick,thereby allowing the side walls 372 of the cavity 368 to help focus thelight emitted from the optical area 336 on the front face 334 of the LED332. The first contact 376 on the front face 334 of the chip is thenelectrically connected to its respective conductive pad 328, such as byusing a wire-bonding technique, as shown in FIG. 7H.

Referring to FIG. 7I, a curable liquid encapsulant 348 is then providedover the first surface 322 of the conductive sheet 320 so as to coverthe LED chip 332, the conductive pads 328 and the wires 344. The curableencapsulant 348 is preferably at least partially transparent ortranslucent and is similar to the encapsulant described above. Theencapsulant 348 is then cured. A transparent lid 354 including a lens360 may be applied in sheet form over the entire assembly or, asdescribed above, may be integrally molded with the top of the package310 using the encapsulant 348 and a suitable mold. Certain surfacefeatures, such as the lenses, may also be molded simultaneously with theinjection molding step so that they are above the optical area 336 onthe front face 334 of the chip 332. Referring to FIG. 7J, the bottomsurface 324 of the conductive sheet 320 is then selectively etched toproduce associated conductive base 326 and conductive pad 328 pairswhich are electrically isolated from one another. Conductive layers 374may be situated so as to act as an etch mask, depending on the materialused for such conductive layers, to aid the selective etching process.The individually packaged LED chips 332 may then be separated from oneanother, as shown in FIG. 7K. Alternately, the packaged devices may beseparated into multichip modules, whereby each module has two or moreside-by-side LED's or light emitting chips.

FIGS. 8A and 8B show a perspective view and a cross-sectional view,respectively, of one preferred embodiment of a package having a LED chipand made in accordance with the techniques described immediately above.The package 310 includes an electrically conductive base 326 having acavity 368 within which a LED chip 332 is placed so that light generatedby the chip 332 may be reflected by the side walls and bottom of thecavity 368 upwardly towards an opening of the cavity 368. The chip 332is inset in the cavity 368 so that side walls 372 of the cavity 368,preferably coated with a metallic conductive layer 374, aid inreflecting light which is emitted from the chip. A first chip contact333 located on the front face 334 of the chip 332 is electricallyconnected to a conductive pad 328 by a conductive wire 344. The rearsurface 340 of the chip 332, having a second electrical contact 341, iselectrically connected to the conductive base 326. The package 310includes a cured encapsulant 348 which is substantially similar to thatdescribed above and which provides structural integrity to the chippackage 310 as well as providing the boundaries of the package.

The package includes an at least partially transparent lid 354juxtaposed with the front face 334 of the chip 332 and attached to thetop surface 352 of the encapsulant 348. As shown in FIG. 8A, the lid 354may include a lens 360 which helps to focus and/or intensify the lightemitted from the chip 322; however, the shape of the lens may be of anystructure that is beneficial to the particular application.

Assembly of the above described chip packages may be accomplished enmass as opposed to the one package at a time methods that areconventionally used today. Basically, the structures described aboveallow for many chips to be attached, bonded and encapsulated in sheetform (i.e. an array of many devices) and simultaneously cut intoindividual devices, parts or groups of devices thereby greatly improvingmanufacturing efficiency.

In a further alternative embodiment of the present invention shown byFIGS. 9A-9H, the conductive pads described above may have a more“rivet-like” shape. FIG. 9A shows a sacrificial layer 420, as earlierdescribed, having a first surface 422 and a second surface 424. Thesacrificial layer 420 is preferably an etchable layer so that cavitiesmay be readily etched into the first surface 422 of the sacrificiallayer 420. Referring to FIG. 9B, a photo-imageable dielectric layer 480,such as standard photoresist, is disposed over the first surface 422 ofthe sacrificial layer 420 and apertures 482 are developed and removedusing standard photo-lithographic techniques so as to control thecreation and placement of the cavities 468.

Referring to FIG. 9C, after the cavities 468 have been formed,conductive pads 428 are next plated into the cavities 468 and apertures482 so as to create the “rivet-like” conductive pads 428. Referring toFIG. 9D, each pad 428 has a bottom bump flange 484 adjacent to thesacrificial layer 420 and integrally attached to a post 486 so that thepost 486 protrudes from the bottom bump flange 484. A second top bumpflange 488 is integrally attached to the opposite end of the post 486.Both bump flanges 484 and 488 have flange areas 490 which extend beyondthe diameter of the post 486. Referring to FIG. 9E, the rear surface 440of a light sensitive chip 432 is then attached to a base 426,electrically connected to the conductive posts 428 and encapsulated withthe at least partially transparent encapsulant, using substantially thesame techniques described above.

FIGS. 10 and 11 show alternate cross-sectional side views of theconductive pads shown in FIGS. 9A-9E according to further embodiments ofthe present invention. In the embodiment shown in FIG. 10, theconductive pad 528 formed atop layer 520 includes a rounded bottom bumpflange 584 and the post 586. In FIG. 11, a conductive pad includingbottom bump flange 684, post 686 and top bump flange 688 are formed atoplayer 620. The bottom and top bump flanges 684 and 688 are more squaredoff at the edges when compared to the rounded/oval bump flanges shown inFIG. 10. Bump flanges having other shapes may also be used.

FIGS. 12A-12F show another embodiment of the present invention includinga process for making a module 710 having a plurality of optoelectronicelements, such as the light emitting chips described above. Referring toFIG. 12A, a substrate 720 includes a dielectric layer 722, such as apolymeric layer, provided between a top conductive layer 724 and abottom conductive layer 726. The top and bottom conductive layers 724and 726 preferably include a highly conductive material such as copper.Referring to FIG. 12B, both the top and bottom conductive layers 724 and726 are preferably coated with photoresist material which is exposed anddeveloped using standard photolithographic techniques. Desirably, afirst layer 728 of the photoresist material having an array of openings730 therein is provided over the top conductive layer 724 and a secondlayer 732 of photoresist material, in the form of an array of pads, isprovided over the bottom conductive layer 726. The array of pads 732 ofphotoresist material over the bottom conductive layer 726 are preferablyin substantial alignment with the openings 730 in the first layer 728 ofphotoresist material. Referring to FIG. 7C, with the first layer 728 ofphotoresist material serving as a mask, portions of the top conductivelayer 724 accessible through the openings 730 are etched away to providepartial vias 734 which extend to the dielectric layer 722. Similarly,the array of pads 732 of photoresist material over the bottom conductivelayer 726 serve as a mask as portions of the bottom conductive layer 726are etched away to provide an array of conductive pads overlying thebottom of the dielectric layer. Referring to FIG. 12D, the photoresistmaterial is then stripped away and the dielectric material 722accessible through the openings 730 in the top conductive layer 724 isetched away so that the conductive pads 736 are accessible throughopenings 738 extending from the top conductive layer 724.

As shown in FIG. 12E, a plurality of LED's 740 are then juxtaposed withthe top conductive layer 724, whereby each LED 740 is preferablypositioned adjacent one of the openings 738 therein. Each LED chippreferably has a front face including a first contact and a rear surfaceincluding a second contact. The rear surfaces of the LED chips 740 arethen assembled to the top conductive layer 724, preferably by using anelectrically conductive adhesive 742, so that the LED chips 740 areelectrically connected to the top conductive layer 724. The topconductive layer 724 will desirably serve as a common ground plane forall of the LED chips 740 which are electrically interconnectedtherewith. Each LED chip 740 is then electrically connected to aconductive pad 736 associated therewith, such as by using a wire-bondingtechnique.

Referring to FIG. 12F, a curable liquid encapsulant 744 may then beprovided over the top conductive layer 724 so as to cover the LED chips740, the wires 746 and the openings 738 extending through the topconductive layer 724 and the dielectric layer 722. The curableencapsulant 744 is preferably at least partially transparent ortranslucent and is similar to the encapsulant described above. Theencapsulant 744 is then cured. A transparent lid (not shown) including alens may be applied in sheet form over the entire assembly or, asdescribed above, may be integrally molded with the top of the packageusing the encapsulant and a suitable mold. The final package 710includes a multichip module having a plurality of LED chips 740.

As these and other variations and combinations of the features describedabove can be utilized without departing from the present invention asdefined by the claims, the foregoing description of the preferredembodiments should be taken by way of illustration rather than by way oflimitation of the invention set forth in the claims.

1. A microelectronic package comprising: a light sensitivemicroelectronic element having a front face including one or morecontacts and a rear surface; conductive leads having first endsconnected to said one or more contacts and second ends connected to oneor more conductive pads adjacent said light sensitive microelectronicelement; an at least partially transparent encapsulant covering saidlight sensitive microelectronic element, said flexible leads and saidone or more conductive pads, said one or more conductive pads beingexposed on a surface of said encapsulant.
 2. The package as claimed inclaim 1, further comprising a base attached to the rear surface of saidlight sensitive microelectronic element, said base being exposed on abottom surface of said encapsulant.
 3. The package as claimed in claim1, said package further comprising an at least partially transparent lidover a top surface of said encapsulant and the front surface of saidlight sensitive microelectronic element.
 4. The package as claimed inclaim 1, wherein said light sensitive microelectronic element is a lightsensitive semiconductor chip.
 4. The package as claimed in claim 1,wherein said light sensitive semiconductor chip includes anultraviolet-erasable programmable read-only memory.
 5. The package asclaimed in claim 1, wherein said package includes two or more of saidlight sensitive microelectronic elements.
 6. The package as claimed inclaim 3, wherein said lid includes a material selected from the groupconsisting of glass, quartz, and rigid polymeric materials.
 7. Thepackage as claimed in claim 6, wherein said lid includes a lens forfocusing light.
 8. The package as claimed in claim 1, wherein saidencapsulant has different levels of transparency.
 9. The package asclaimed in claim 1, wherein said encapsulant includes a color tintedportion.
 10. The package as claimed in claim 1, wherein said encapsulantis more transparent in one portion of said package and less transparentin another portion of said package.
 11. The package as claimed in claim1, wherein said encapsulant includes a compliant material.
 12. Thepackage as claimed in claim 1, wherein the compliancy of saidencapsulant varies throughout said package.
 13. The package as claimedin claim 1, wherein said encapsulant adjacent said conductive pads isless compliant than said encapsulant adjacent said contacts on saidlight sensitive microelectronic element.
 14. A microelectronic packagecomprising: an electrically conductive base having a cavity formed in atop surface thereof; a conductive pad adjacent said conductive base; alight sensitive microelectronic element disposed in said cavity, saidoptoelectronic element having a front face including a first contact anda rear surface including a second contact, said second contact beingelectrically connected to said conductive base; a conductive lead havinga first end connected to said first contact and a second end connectedto said conductive pad; an at least partially transparent encapsulantcovering said light sensitive microelectronic element, said base, saidlead and said conductive pad, said conductive base and said conductivepad being exposed on a bottom surface of said encapsulant, the bottomsurface of said encapsulant defining the bottom of said package.